Human adenoviruses in children with gastroenteritis: a systematic review and meta-analysis

Purpose Human adenoviruses (HAdVs) have always been suggested as one of the main causes of gastroenteritis in children. However, no comprehensive report on the global epidemiology of these viruses in pediatric gastroenteritis is available. Methods A systematic search was conducted to obtain published papers from 2003 to 2023 in three main databases PubMed, Scopus, and Web of Science. Results The estimated global pooled prevalence of HAdV infection in children with gastroenteritis was 10% (95% CI: 9-11%), with a growing trend after 2010. The highest prevalence was observed in Africa (20%, 95% CI: 14–26%). The prevalence was higher in inpatients (11%; 95% CI: 8-13%) and patients aged 5 years old and younger (9%; 95% CI: 7-10%). However, no significant difference was observed between male and female patients (P = 0.63). The most prevalent species was found to be the species F (57%; 95% CI: 41-72%). The most common HAdVs observed in children with gastroenteritis were types 40/41, 38, and 2. Analysis of case-control studies showed an association between HAdV and gastroenteritis in children (OR: 2.28, 95% CI; 1.51–3.44). Conclusion This study provided valuable insights into the importance of HAdVs in children with gastroenteritis, especially in hospitalized and younger children. The results can be used in future preventive measurements and the development of effective vaccines. Supplementary Information The online version contains supplementary material available at 10.1186/s12879-024-09386-x.


Introduction
Acute gastroenteritis is a serious threat to health that affects individuals of any age.It is especially serious for the very young, such as newborns and young children [1,2].Because of their underdeveloped immunity, children are more susceptible to diarrheal illnesses.Different enteric pathogens, including bacteria, viruses, protozoa, helminths, and fungi, can cause diarrhea.These pathogens are typically transmitted by ingesting contaminated food, water, or things infected with feces [3].Previous studies have shown that the virus is the most common cause of acute gastroenteritis in individuals younger than 18 years of age [4,5].The most common causes of acute gastroenteritis in children are rotavirus, norovirus (NoV), human adenovirus (HAdV), and human astrovirus (HAstV) [6,7].
HAdV is a member of the Adenoviridae family and the Mastadenovirus genus.HAdV is a non-enveloped, medium-sized virus (70-100 nm) with an icosahedral nucleocapsid that contains a 34-45 kbp double-stranded linear DNA genome [8,9].HAdVs have been divided into seven species A to G based on pathogenicity and genetic features, with 115 distinct HAdVs genotypes being identified [10].Based on the percentage of guanine plus cytosine in their DNA and other biochemical and biophysical criteria which are classified into 7 species (A-G).The word serotype is used to point to types up to 51 while newer types, which were differentiated by novel sequences or recombinant phylogeny in genes coding for major capsid proteins are known as genotype.Species G is composed of one type (type 52) and is extremely rare while other species are found in patients with various diseases including gastroenteritis, conjunctivitis, respiratory infections, and to a lesser extent in intussusception in infants, hemorrhagic cystitis, meningoencephalitis, myocarditis, and hepatitis [11].HAdV infection, a highly infectious disease, can infect a range of organs, including upper and lower respiratory tracts, gastrointestinal tract, urinary tract, eye, and other systems [11]. .Tissue tropisms vary by species.It has been determined that the primary cause of acute gastroenteritis among the seven species is the HAdV F species, also known as enteric HAdV, which contains the HAdV-F40 and HAdV-F41 genotypes [12][13][14][15].Enteric species F (genotypes F40/41) strains were predicted using a mathematical model to be the third most common agent responsible for mortality in diarrheal children under the age of five, after rotavirus and Shigella [16].Furthermore, stool samples from patients with acute gastroenteritis have regularly revealed the presence of several other non-enteric HAdV species (HAdV A-E and G species), including HAdV A, B, C, and D [12,13,15,[17][18][19][20].
While there are many reports from different parts of the world, there is a gap of knowledge in understanding the epidemiology and association of HAdVs and pediatric gastroenteritis.This study aims to fulfill this gap by comprehensively analysis various factors including age group, gender, geographical teacher, clinical setting, diagnostics methods, species, and genotypes in pediatrics gastroenteritis for the first time to provide valuable insights into the current status of HAdVs in children with gastroenteritis.

Methods
The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline served as the foundation for this systematic review and meta-analysis approach [21].

Search strategy
To discover relevant papers, a systematic literature search was undertaken utilizing three electronic databases including PubMed, Scopus, and Web of Science.The literature search was restricted to the period between inception to June 24, 2023.Table S1 provides information about the search terms for each database.We manually searched the reference lists of pertinent articles to find further research that met the eligibility criteria.For data management, the systematic literature search was loaded into EndNote software version X8 (Thomson Reuters, California, USA).

Selection criteria
Studies were considered qualified if they reported: (1) case-control and cross-sectional studies providing data related to the prevalence of enteric and non-enteric HAdVs among children less than 18 years with gastroenteritis published in the English language in peer-reviewed journals; (2)

Data extraction and quality assessment
Two reviewers separately examined the titles and abstracts of all identified papers, and studies that were unrelated to the study topic were eliminated.The reviewers got full texts of the selected papers and further analyzed them, and those that did not meet the inclusion criteria were excluded.Finally, any differences among reviewers were settled by consulting with a third reviewer.Utilizing a modified checklist based on strengthening the reporting of observational studies in epidemiology (STROBE), a quality assessment of the retrieved studies was carried out [22,23].The checklist consisted of 12 questions that addressed various methodological approaches.Studies that received a validity score of at least 8 out of a maximum of 12 were considered eligible for the main meta-analysis.One reviewer extracted the data listed below from each eligible article: first author's last name, year of publication, year of sampling, study location, study design, sample size, age ranges of patients, age groups of patients, the gender of patients, number of HAdV-positive cases, HAdV detection methods, types of patient care, species, and genotype of HAdV.The retrieved data were entered into a pre-designed Excel spreadsheet (Microsoft Corporation, Redmond, Washington, USA).

Statistical analysis
We pooled the HAdV infection in children suffering from gastroenteritis using the metaprop package [24].We applied the random-effects meta-analysis framework and subgroup analysis was conducted based on region, gender, age, detection method, sampling time, types of patient care, and genotype of HAdV.We also conducted meta-analyses of risk estimates for gastroenteritis and exposure to HAdV, and we reported pooled estimates of odds ratio (OR) and 95% CIs.DerSimonian and Laird method was used to compute the pooled estimate of OR with confidence interval (95% CI) using random models.Statistical heterogeneity between studies was evaluated with Cochran's Q test and quantified by I 2 statistic [25].We investigated the presence and the effect of publication bias using a combination of the visual inspection of funnel plots that were constructed, plotting the logarithmically transformed ORs against the standard error of the associated log (OR) and Begg's test and Egger's test.All statistical tests were two-tailed and the significance level was considered less than 0.05 for all, except heterogeneity test that were set at less than 0.1, and statistical analyses were performed using Stata 14.1 (Stata Corp, College Station, TX, USA).

Literature search
During the initial search, 3733 papers were identified, and 40 further papers were discovered by manually examining the reference lists of pertinent research.A total of 1592 duplicate papers were initially removed, and 1766 additional papers were removed after a manual check of titles and abstracts.After a thorough evaluation of the full text of the remaining 415 papers to determine their eligibility for the meta-analysis, 251 of them were removed.According to the modified STROBE checklist, 155 publications were deemed to be of good quality (scoring of 8 or higher), with 9 papers were failed to get a score of 8. Finally, this systematic review and meta-analysis contained 155 papers.An overview of the selection of relevant studies is depicted in Fig. 1.

Study characteristics
Out of the 155 studies considered, 134 were cross-sectional and 21 were case-control in design.The articles' publication dates varied from 2003 to 2023.The largest research involved 85,001 gastroenteritis cases [26], while the smallest contained 24 cases [27].Out of the 155 papers included in this meta-analysis, 19 research examined the gender distribution of HAdV infection, and 80 studies looked into the genotype distribution of HAdVs.Specific primers for the detection of HAdVs group F (types 40 and 41) and universal primers identifying all types of HAdVs have been used in 37 and 118 studies, respectively.The majority of study populations (n = 103,815) were children under 5 years of age and 12,982 were children between the ages of 6 and 18 years old.The majority of studies (n = 29) were conducted in China, followed by Brazil (n = 12), India (n = 11), and Japan (n = 10).Regarding the continent, 84 were conducted in Asia, 26 in South America, 18 in Europe, 16 in North America, 9 in Africa, and 2 in Oceania.The characteristics of included studies in this systematic review and meta-analysis are summarized in Table 1.
A time trend analysis was conducted to assess variations in the prevalence of HAdV infection over time throughout the world.According to this analysis, the prevalence of HAdV was the highest (32%; 95% CI:

Prevalence of HAdV infection before and after coronavirus disease 2019 (COVID-19)
Our analysis indicated that the prevalence of HAdV among children with gastroenteritis in studies with the sampling time in 2019 and earlier was (10%, 95% CI: 9-11%) while the prevalence in studies with sampling time from 2020 and later was (13%, 95% CI: 6-21%), showing a statistically significant difference (P < 0.001).

Association of HAdV infection with gastroenteritis among children
The second analysis used data from case-control studies to look into the relationship between HAdV infection and the risk of gastroenteritis in children.There were 10,482 gastroenteritis patients and 7618 controls in 21 case-control studies.The results showed that the overall pooled odds ratio (OR) of the association of HAdV infection (detected by universal + species F primers) and gastroenteritis was 2.29 (95% CI: 1.52-3.44;I 2 = 89.6%)(Fig. 4).
Based on the funnel plot (Fig. 5) there was no evidence of publication bias in the meta-analysis, which was statistically supported by Begg's test (p = 0.55) and Egger's test (p = 0.82).

Sensitivity analysis
In a sensitivity analysis by successively removing a particular study at a time to assess the influence of every single study on pooled results, a significant positive association [range of summary ORs 2.14-2.43]between HAdV infection and gastroenteritis among children was observed consistently and did not alter the pooled results, which indicated that the meta-analysis model is robust.

Discussion
Acute gastroenteritis is still a prominent global health threat for children, especially in developing countries.In recent years, the improvements in sanitation have led to a decrease in the prevalence of bacterial and parasitical agents in the development of acute gastroenteritis, making viruses the main causative agent of the disease.While individuals of all ages can be infected by HAdVs, children are the main targets of these viruses.To the best of our knowledge, no systematic review and meta-analysis has been performed on the prevalence of HAdVs and pediatric patients with gastroenteritis.Our results showed a high (10%) prevalence of HAdVs in children with gastroenteritis, which highlights the role of HAdVs as a main cause of gastroenteritis among children worldwide.While rotavirus was known as the main cause of pediatric gastroenteritis, the introduction of rotavirus vaccine is changing the pattern [174,175].We exhibited a higher prevalence of HAdVs infection in studies published after 2010, which show the increasing trend of HAdVs in the pathogenesis of pediatric gastroenteritis.Furthermore, the analysis of case-control studies indicated an association (OR: 2.28, 95% CI; 1. 51-3.44) between HAdV infection and gastroenteritis in children.Therefore, in addition to respiratory infections [176], HAdVs are important pathogens in gastroenteritis among children.
Among the different regions, the highest prevalence was observed in Africa.Low micronutrition (such as vitamins and trace elements) intake as a result of Fig. 4 Forest plot of the association between HAdV infection and gastroenteritis risk in pediatric patients according to the random effect model in case case-control studies using universal and F primers for the detection of HAdV malnutrition is a key factor that abates the ability of both innate and adaptive immune systems to fight pathogens [177].Also, poor sanitation and hygiene can be a key contributor that facilitates the infection of the gastrointestinal tract by enteric viruses [178].Other continents with high prevalence were South America and Oceania.Therefore, our results delineate an epidemiologic pattern with higher prevalence in the southern hemisphere.This can be due to malnutrition and lack of proper hygiene, which make children prone to infectious gastroenteritis by negatively affecting the immune system and exposing children to viral agents [174].Interestingly, there was a significantly higher prevalence of HAdV in pediatric gastroenteritis cases after the initiation of the COVID-19 pandemic.It might be due to the fact that despite the effects of social distancing and mask mandate on respiratory infections, their effects on preventing viral gastroenteritis were limited and in some regions, schools were less focused on preventing gastroenteritis and therefore, school authorities could not efficiently report gastroenteritis cases, which enables the viruses to be transmitted to other children [179].Moreover, the rise of malnutrition due to financial restrictions and lack of access to school meals for children [180] is another factor, which makes children more vulnerable to viral infection by weakening the immune system [181].
Our results did not indicate a significant difference (P value = 0.06) between male and female patients.This suggests that the occurrence of HAdVs-related gastroenteritis does not exhibit a gender-based pattern among children.After puberty, different compartments of the immune system are affected by sex hormones.For example, androgens including dihydrotestosterone (DHT) and testosterone can suppress immune cell activities in postpubertal individuals [182].However, the impacts of sex hormones are not significant in this study due to the age of the included patients.Studies on various viral infections in children resulted in different results and therefore, a specific sex is not prone to viral infections [183].
Exploring the age-specific prevalence of HAdVs in pediatric gastroenteritis showed intriguing patterns in the distribution of infections across different age groups.Notably, the prevalence of HAdVs was significantly higher (P < 0.001) in children younger than 5 years old, which shows the higher susceptibility of this age group.This difference aligns with the well-established notion Fig. 5 Funnel plot for assessment of publication bias that young children are more susceptible to viral infections.This vulnerability is primarily due to the immaturity of their immune systems, which does not provide robust protection against viral pathogens [184].Additionally, younger children often have limited pre-existing immunity and may lack previous exposure to HAdVs, which makes them more prone to infection [185].The increased possibility of close contact in daycare settings, preschools, and households may further contribute to a higher risk of transmission in this age group.As children advance to later childhood, their immune systems become more mature [184] and exposure in early life fosters a natural immunity to pathogens [174,184].Behavioral changes such as improved hygiene practices may also help the reduction of the risk of diarrhea [186].These findings highlight the importance of monitoring HAdV transmission and infection in childcare and healthcare settings to avoid future outbreaks.
More than half of typed HAdVs in our study belonged to species F, which consisted of types 40/41 that are known for their role in gastroenteritis [11].In addition, no significant difference (P = 0.06) was observed between universal primers and those that were designed to only detect species F, which shows the remarkable prevalence of this species in HAdVs-related gastroenteritis cases.Interestingly, we observed that species C, which is known to cause respiratory symptoms [11], is the second most prevalent species in pediatric gastroenteritis cases.This underscores the clinical importance of species C as a causative agent of respiratory and gastrointestinal infections among children.These data are good indicators of the most prevalent species and can be used to design effective vaccines.
In the context of clinical settings, the pooled prevalence for inpatients was found to be slightly higher than the prevalence among outpatients.While this difference did not reach statistical significance (P = 0.09), the trend suggests a potential association between HAdV infections and increased disease severity necessitating hospitalization.Noteworthy, the lack of statistical significance may stem from various factors, including heterogeneity in study populations, variations in healthcare practices, and potential underreporting in outpatient settings.Further research into the specific factors contributing to the observed prevalence differences between inpatients and outpatients can provide valuable insights into the clinical implications of HAdVs-associated gastroenteritis.
This systematic review and meta-analysis faced some limitations.There were no studies from some countries in various geographic regions such as Africa and Europe.We recommend researchers to conduct epidemiologic studies in those countries with no previous reports to gain a comprehensive insight into the HAdV epidemiology in pediatric gastroenteritis.Some reports did not mention the characteristics of isolated viruses including species and genotypes.Finally, in the context of systematic review and meta-analysis studies, publication bias and study heterogeneity are inevitable limitations.

Conclusion
This systematic review and meta-analysis highlights HAdVs as significant and increasing causes of pediatric gastroenteritis globally, particularly affecting children under 5 years old.The prevalence is considerably high in Africa, with also remarkable rates in South America and Oceania, which shows a southern hemisphere predominance possibly linked to factors such as malnutrition and poor sanitation.Furthermore, the absence of a genderbased pattern suggests equal susceptibility among male and female pediatric patients.Variations in diagnostic approaches indicate the importance of choosing sensitive tests such as Nested PCR.The dominance of species F adenoviruses, genotypes 40/41, shows potential targets for vaccine development.A higher prevalence among inpatients can be indicative of the potential of HAdVs to cause severe gastrointestinal symptoms.These results suggest future epidemiologic investigations, particularly in underrepresented regions to address existing gaps in HAdVs epidemiology in pediatric gastroenteritis.

Fig. 1
Fig. 1 Flowchart presenting the steps of literature search and selection Figure 2 depicts the global distribution of HAdV infection among children with gastroenteritis.With respect to HAdV detection methods, Nested PCR, Multiplex PCR, Real-time PCR, Conventional PCR, and Multiplex Real-time PCR methods were used.

Fig. 2
Fig. 2 The global map presents the geographical variations in the prevalence of HAdV infection among pediatric patients with gastroenteritis in a period of 11 years (2003-2023)

Fig. 3
Fig. 3 Distribution of HAdV types in children with gastroenteritis

Table 1
Characteristics of studies included in the systematic review and meta-analysis

Table 2
Subgroup analysis of the prevalence of HAdV infection among pediatric patients with gastroenteritis